1. Field of the Invention
The present invention relates generally to a control apparatus for a motor vehicle. More particularly, the invention is concerned with a control apparatus for electrically controlling a throttle vale of an internal combustion engine for a motor vehicle.
2. Description of the Related Art
In a conventional throttle valve control apparatus of an internal combustion engine (hereinafter also referred to simply as the engine) for an automobile or a motor vehicle, a throttle valve is mechanically linked to an accelerator pedal in such a manner that the opening degree of the throttle valve can controllably be changed in dependence on the magnitude or amount of depression of the accelerator pedal. More particularly the opening degree of the throttle valve is electrically controlled through a throttle actuator in dependence on amount of depression of an accelerator pedal and the speed of the motor vehicle, as is disclosed, for example, in Japanese Kokai No. 261635/1986 (JP-A-61-261635). The structure of this conventional throttle valve control apparatus is shown in functional block diagram FIG. 6.
Referring to FIG. 6, the conventional control apparatus is basically comprised of a vehicle speed sensor 2 for detecting the speed of a motor vehicle equipped with this control apparatus, a control means 5 for controlling a throttle actuator 6 on the basis of both an actual throttle opening signal representative of the actual opening degree of a throttle valve, and a target throttle opening signal representative of a target opening degree of the throttle valve inputted to the control means 5, as well as a vehicle speed signal, as described hereinafter, a throttle valve 7 whose opening degree is rotationally controlled by the throttle actuator 6 and a throttle opening sensor 8 for detecting the opening degree of the throttle valve 7.
Further, the throttle control apparatus is equipped with an accelerator pedal depression detecting means 21 for detecting the depression of an accelerator pedal (not shown) of the motor vehicle, a function generator 22 having inputs supplied, respectively, with an accelerator pedal depression signal S.sub.1 from the accelerator pedal depression detecting means 21 and a throttle response signal (or acceleration response signal, stated another way). The function generator determines a relation between the depth of depression of the accelerator pedal and a target throttle valve opening on the basis of the acceleration response signal AG. The throttle control apparatus additionally comprises an average throttle valve opening calculating means 23 for arithmetically determining an average or mean value of the throttle valve 7 during a preceding predetermined period of running of the motor vehicle at predetermined intervals. Also provided are an average vehicle speed calculating means for arithmetically determining a means vehicle speed over a predetermined time at predetermined intervals, and an acceleration response calculating means for arithmetically determining an acceleration response or throttle response indicative of the sensitivity or response of the throttle valve 7 to the actuation or depression of the accelerator pedal on the basis of the average vehicle speed signal and the average throttle opening signal. The throttle actuator 6 is so controlled by the control means 5 that the opening degree of the throttle valve 7 becomes equal to the target or command value. For more particulars of the individual components of this known control apparatus, reference should be made to the publication mentioned hereinbefore.
In operation of the throttle opening control apparatus of the structure described above, the depression of the accelerator pedal actuated by the driver is detected by the accelerator pedal depression detecting means 21, whereby the opening of the throttle valve 7 is controlled in dependence on the accelerator pedal depression in accordance with a given functional relationship. To this end, the function generator 22 generates a functional relation between the accelerator pedal depression and the throttle opening on the basis of the acceleration response signal outputted from the unit 25, to thereby issue a target throttle opening command signed to control means 5. The acceleration response signal represents the relation between the average or mean vehicle speed and the mean throttle valve opening control means 5 then responds by controlling the throttle opening through the throttle actuator 6 which may be constituted by a stepping motor, a DC motor or the like and a gear train.
In this conjunction, for a given opening degree of the throttle valve, the vehicle speed will vary in dependence on changes in the load imposed on the motor vehicle. This experienced when the vehicle is driven to run on a road abounding with uphills and downhills. To compensate for such variations in the load on the control of the throttle opening, the mean throttle opening as well as the mean vehicle speed successively determined for a predetermined period at predetermined intervals are adopted as correcting parameters. For example, the function generator 22 generates a function which acts as follows. Namely, if the mean vehicle speed is low for a predetermined period notwithstanding of a large value of the mean throttle opening, it is determined that the vehicle is subject to a large load, that is the vehicle is travelling on an uphill. In this case, the function generated for throttle control is such that it increased the throttle opening to a value greater than a normal value which is obtained during a normal running state of the vehicle in which the vehicle travels on a level road. On the other hand, if the mean value is high for the predetermined period in spite of a small value of the mean throttle opening, it is determined that the load on the vehicle is small, that is the vehicle is travelling on a downhill. In this case, the function generated is such that it decreased the throttle opening to a value smaller than the normal value.
As is apparent from the foregoing, with the above-mentioned conventional throttle valve control apparatus, the throttle opening control is conducted by detecting not only the pedal depression depth which represents a target vehicle speed commanded by the driver but also the actual vehicle speed which is subjected to variations in dependence on the running state or load condition of the motor vehicle to thereby control the throttle opening so that it reflects the target vehicle speed, in an endeavor to enhance the drivability or maneuverability of the motor vehicle.
However, with such control, information about the gear ratio or gear position of the motor vehicle is not employed or reflected, so it is difficult to realize an enhanced accelerating ability as well as maneuverability intrinsically required for the motor vehicle. In fact, even with the same vehicle speed and the same throttle opening, acceleration performance of the vehicle significantly varies in dependence upon the gear ratio or gear position.
Besides, in the above-mentioned conventional control apparatus, no reasonable consideration is paid to the possibility of occurrence of a failure in the throttle valve control apparatus and more particularly a failure in the throttle actuator 6, the throttle opening sensor 8 or the like. Thus, if the throttle actuator 6 fails with the throttle valve being held open, or if the throttle opening sensor 8 fails while continuously generating an output signal indicative of an open position of the throttle valve 7, the vehicle will cause a runaway.
Accordingly, there exists a demand for solving the above problems from which the conventional throttle control apparatus for the motor vehicle suffers.